Prediction of tin-whiskers generation during thermal cycle test using stress and mass-diffusion analysis

A previously developed simulation technique has been applied to the prediction of the location of tin whiskers, which create reliability problems, generated on electrodeposited tin plating on a copper lead frame. This multi-scale simulation technique uses molecular dynamics simulation and a finite element method (FEM). The FEM model is used to simulate stress and stress-induced mass diffusion, including grain-boundary diffusion, in tin plating. The stress analysis model considers elasticity anisotropy, thermal-expansion anisotropy, and the crystal orientation of s-tin. A thermal cycling test was conducted to induce whisker generation on tin-plated specimens, and the crystalline orientations around the whiskers were evaluated using electron back-scattering diffraction pattern (EBSP) measurement. The hydrostatic pressure distribution and tin-atomic-density distribution in the specimens were calculated using a simulation technique that considers the crystal orientations of the β-tin grains determined using EBSP measurement. The results were used to investigate the relationship between the tin-atomic-density distribution and whisker locations. The whisker locations corresponded to the areas of higher tin-atomic density and lower hydrostatic pressure on the tin-plated surface, indicating that the previously developed simulation technique can be used to predict the location of whiskers generated on tin plating.